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    //! `GenericArray` iterator implementation.

    use super::{ArrayLength, GenericArray};
    use core::{cmp, ptr, fmt, mem};
    use core::mem::ManuallyDrop;

    /// An iterator that moves out of a `GenericArray`
    pub struct GenericArrayIter<T, N: ArrayLength<T>> {
        // Invariants: index <= index_back <= N
        // Only values in array[index..index_back] are alive at any given time.
        // Values from array[..index] and array[index_back..] are already moved/dropped.
        array: ManuallyDrop<GenericArray<T, N>>,
        index: usize,
        index_back: usize,
    }

    #[cfg(test)]
    mod test {
        use super::*;

        fn send<I: Send>(_iter: I) {}

        #[test]
        fn test_send_iter() {
            send(GenericArray::from([1, 2, 3, 4]).into_iter());
        }
    }

    impl<T, N> GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        /// Returns the remaining items of this iterator as a slice
        #[inline]
        pub fn as_slice(&self) -> &[T] {
            &self.array.as_slice()[self.index..self.index_back]
        }

        /// Returns the remaining items of this iterator as a mutable slice
        #[inline]
        pub fn as_mut_slice(&mut self) -> &mut [T] {
            &mut self.array.as_mut_slice()[self.index..self.index_back]
        }
    }

    impl<T, N> IntoIterator for GenericArray<T, N>
    where
        N: ArrayLength<T>,
    {
        type Item = T;
        type IntoIter = GenericArrayIter<T, N>;

        fn into_iter(self) -> Self::IntoIter {
            GenericArrayIter {
                array: ManuallyDrop::new(self),
                index: 0,
                index_back: N::to_usize(),
            }
        }
    }

    // Based on work in rust-lang/rust#49000
    impl<T: fmt::Debug, N> fmt::Debug for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_tuple("GenericArrayIter")
                .field(&self.as_slice())
                .finish()
        }
    }

    impl<T, N> Drop for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        #[inline]
        fn drop(&mut self) {
            // Drop values that are still alive.
            for p in self.as_mut_slice() {
                unsafe {
                    ptr::drop_in_place(p);
                }
            }
        }
    }

    // Based on work in rust-lang/rust#49000
    impl<T: Clone, N> Clone for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        fn clone(&self) -> Self {
            // This places all cloned elements at the start of the new array iterator,
            // not at their original indices.
            unsafe {
                let mut iter = GenericArrayIter {
                    array: ManuallyDrop::new(mem::uninitialized()),
                    index: 0,
                    index_back: 0,
                };

                for (dst, src) in iter.array.iter_mut().zip(self.as_slice()) {
                    ptr::write(dst, src.clone());

                    iter.index_back += 1;
                }

                iter
            }
        }
    }

    impl<T, N> Iterator for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        type Item = T;

        #[inline]
        fn next(&mut self) -> Option<T> {
            if self.index < self.index_back {
                let p = unsafe { Some(ptr::read(self.array.get_unchecked(self.index))) };

                self.index += 1;

                p
            } else {
                None
            }
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            let len = self.len();
            (len, Some(len))
        }

        #[inline]
        fn count(self) -> usize {
            self.len()
        }

        fn nth(&mut self, n: usize) -> Option<T> {
            // First consume values prior to the nth.
            let ndrop = cmp::min(n, self.len());

            for p in &mut self.array[self.index..self.index + ndrop] {
                self.index += 1;

                unsafe {
                    ptr::drop_in_place(p);
                }
            }

            self.next()
        }

        fn last(mut self) -> Option<T> {
            // Note, everything else will correctly drop first as `self` leaves scope.
            self.next_back()
        }
    }

    impl<T, N> DoubleEndedIterator for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        fn next_back(&mut self) -> Option<T> {
            if self.index < self.index_back {
                self.index_back -= 1;

                unsafe { Some(ptr::read(self.array.get_unchecked(self.index_back))) }
            } else {
                None
            }
        }
    }

    impl<T, N> ExactSizeIterator for GenericArrayIter<T, N>
    where
        N: ArrayLength<T>,
    {
        fn len(&self) -> usize {
            self.index_back - self.index
        }
    }

    // TODO: Implement `FusedIterator` and `TrustedLen` when stabilized

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